Use of encapsulated acid in acid fracturing treatments

Abstract

A method of fracturing a subterranean formation, in which subterranean formation being in fluid communication with the surface includes creating a fracture in said subterranean formation, said fracture having more than one fracture faces; and injecting into said fracture an encapsulated formation etching agent, wherein said encapsulated formation etching agent includes a formation etching agent and an encapsulating agent and wherein said formation etching agent etches the fracture faces of the fracture so as to form a flow channel in said formation. The formation etching agent may be selected from mineral acids and mixtures thereof, organic acids and mixtures thereof, mineral acids and mixtures of mineral acids mixed with gelling agent, organic acids and mixtures of organic acids mixed with gelling agent, water soluble hydroxides and mixtures of water soluble hydroxides, and water soluble hydroxides and mixtures of water soluble hydroxides mixed with gelling agent. The encapsulating agent may be a natural and synthetic oils, natural and synthetic polymers and enteric polymers and mixtures thereof.

What is claimed is:  
     
       1. A method of fracturing a subterranean formation, said subterranean formation being in fluid communication with the surface, said method comprising: 
       creating a fracture in said subterranean formation, said fracture having more than one fracture faces; and  
       injecting into said fracture an encapsulated formation etching agent, wherein said encapsulated formation etching agent includes a formation etching agent and an encapsulating agent and wherein said formation etching agent etches the fracture faces of the fracture so as to form a flow channel in said formation.  
     
     
       2. The method of claim  1  wherein the formation etching agent is selected from: mineral acids and mixtures thereof, organic acids and mixtures thereof, mineral acids and mixtures of mineral acids mixed with gelling agent, organic acids and mixtures of organic acids mixed with gelling agent, water soluble hydroxides and mixtures of water soluble hydroxides, and water soluble hydroxides and mixtures of water soluble hydroxides mixed with gelling agent. 
     
     
       3. The method of claim  2  wherein the formation etching agent is selected from: hydrochloric acid, hydrofluoric acid, hydrochloric and hydrofluoric acid mixtures, hydrochloric acid mixed with gelling agent, hydrofluoric acid mixed with gelling agent, acetic acid, formic acid, acetic acid mixed with gelling agent, formic acid mixed with gelling agent, citric acid, alkali metal hydroxides and mixtures of alkali metal hydroxides, alkaline earth metal hydroxides and mixtures of alkaline earth metal hydroxides, lime and mixtures of lime with other basic metal oxides and hydroxides, alkali metal hydroxides and mixtures of alkali metal hydroxides mixed with gelling agent, alkaline earth metal hydroxides and mixtures of alkaline earth metal hydroxides mixed with gelling agent, lime and mixtures of lime with other basic metal oxides and hydroxides and gelling agent. 
     
     
       4. The method of claim  1  wherein the encapsulating agent is selected so as to encapsulate said formation etching agent thus reducing chemical reactivity and so as to release said formation etching agent under predetermined conditions of temperature, pressure, pH, abrasion or combinations thereof. 
     
     
       5. The method of claim  4  wherein the encapsulating agent is selected from natural and synthetic oils, natural and synthetic polymers and enteric polymers and mixtures thereof. 
     
     
       6. The method of claim  1  wherein the encapsulated formation etching agent has a density less than sand. 
     
     
       7. A method of acid fracturing a subterranean formation, said subterranean formation being in fluid communication with the surface, said method comprising: 
       injecting into said formation a pad fluid, said pad fluid being under a hydraulic pressure sufficient to create an open fracture in said formation, said open fracture having one or more fracture faces;  
       injecting into said open fracture an encapsulated formation etching agent, said encapsulated formation etching agent including a formation etching agent being encapsulated by an encapsulating agent, wherein said formation etching agent is capable of etching the fracture faces of said formation;  
       etching the fracture faces with said formation etching agent so as to give one or more etched fracture faces; and  
       releasing the hydraulic pressure on the formation so as to close the open fracture thus forming one or more flow channels, said flow channels being defined by the etched fracture faces.  
     
     
       8. The method of claim  7  wherein the formation etching agent is selected from: mineral acids and mixtures thereof, organic acids and mixtures thereof, mineral acids and mixtures of mineral acids mixed with gelling agent, organic acids and mixtures of organic acids mixed with gelling agent, water soluble hydroxides and mixtures of water soluble hydroxides, and water soluble hydroxides and mixtures of water soluble hydroxides mixed with gelling agent. 
     
     
       9. The method of claim  8  wherein the formation etching agent is selected from: hydrochloric acid, hydrofluoric acid, hydrochloric and hydrofluoric acid mixtures, hydrochloric acid mixed with gelling agent, hydrofluoric acid mixed with gelling agent, acetic acid, formic acid, acetic acid mixed with gelling agent, formic acid mixed with gelling agent, citric acid, alkali metal hydroxides and mixtures of alkali metal hydroxides, alkaline earth metal hydroxides and mixtures of alkaline earth metal hydroxides, lime and mixtures of lime with other basic metal oxides and hydroxides, alkali metal hydroxides and mixtures of alkali metal hydroxides mixed with gelling agent, alkaline earth metal hydroxides and mixtures of alkaline earth metal hydroxides mixed with gelling agent, lime and mixtures of lime with other basic metal oxides and hydroxides and gelling agent. 
     
     
       10. The method of claim  7  wherein the encapsulating agent is selected so as to encapsulate said formation etching agent thus reducing chemical reactivity and so as to release said formation etching agent under predetermined conditions of temperature, pressure, pH, abrasion or combinations thereof. 
     
     
       11. The method of claim  10  wherein the encapsulating agent is selected from natural and synthetic oils, natural and synthetic polymers and enteric polymers and mixtures thereof. 
     
     
       12. The method of claim  7  wherein the encapsulated formation etching agent has a density less than sand. 
     
     
       13. A method of increasing the production of hydrocarbon fluids from a hydrocarbon fluid bearing subterranean formation, said formation being in fluid communication with the surface by way of a well, said method comprising: 
       injecting into said formation a pad fluid by way of said well;  
       pressurizing said pad fluid so as to create open fractures in said subterranean formation, said fractures having one or more fracture faces;  
       injecting into said open fractures a formation treating composition, said formation treating composition including an encapsulated formation etching agent and a carrier fluid, said encapsulated formation etching agent including a formation etching agent being encapsulated by an encapsulating agent and wherein said formation etching agent being capable of etching the fracture faces of said formation;  
       shutting-in said well for a sufficient time so as to allow said formation treating agent to be released from said encapsulating agent thus etching said fracture faces and giving etched fracture faces; and  
       depresurizing said fluid so as to close the open fractures thus forming one or more flow channels, said flow channels being defined by the etched fracture faces, wherein said flow channels increase the production of hydrocarbon fluids from said hydrocarbon fluid bearing subterranean formation.  
     
     
       14. The method of claim  13  wherein the formation etching agent is selected from: mineral acids and mixtures thereof, organic acids and mixtures thereof, mineral acids and mixtures of mineral acids mixed with gelling agent, organic acids and mixtures of organic acids mixed with gelling agent, water soluble hydroxides and mixtures of water soluble hydroxides, and water soluble hydroxides and mixtures of water soluble hydroxides mixed with gelling agent. 
     
     
       15. The method of claim  14  wherein the formation etching agent is selected from: hydrochloric acid, hydrofluoric acid, hydrochloric and hydrofluoric acid mixtures, hydrochloric acid mixed with gelling agent, hydrofluoric acid mixed with gelling agent, acetic acid, formic acid, acetic acid mixed with gelling agent, formic acid mixed with gelling agent, citric acid, alkali metal hydroxides and mixtures of alkali metal hydroxides, alkaline earth metal hydroxides and mixtures of alkaline earth metal hydroxides, lime and mixtures of lime with other basic metal oxides and hydroxides, alkali metal hydroxides and mixtures of alkali metal hydroxides mixed with gelling agent, alkaline earth metal hydroxides and mixtures of alkaline earth metal hydroxides mixed with gelling agent, lime and mixtures of lime with other basic metal oxides and hydroxides and gelling agent. 
     
     
       16. The method of claim  13  wherein the encapsulating agent is selected so as to encapsulate said formation etching agent thus reducing chemical reactivity and so as to release said formation etching agent under predetermined conditions of temperature, pressure, pH, abrasion or combinations thereof. 
     
     
       17. The method of claim  16  wherein the encapsulating agent is selected from natural and synthetic oils, natural and synthetic polymers and enteric polymers and mixtures thereof. 
     
     
       18. The method of claim  13  wherein the encapsulated formation etching agent has a density less than sand.